Q.

If y=cos 6x+6cos 4x+15cos 2x+10cos 5x+5cos 3x+10cos x then dydx=

Moderate

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By Expert Faculty of Sri Chaitanya

a

2sin x+cos x

b

-2sin x

c

cos 2x

d

sin 2x

answer is B.

(Detailed Solution Below)

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Detailed Solution

y=(cos 6x+cos 4x)+5(cos 4x+cos 2x)+10(cos 2x+1)cos 5x+5cos 3x+10cos x=2cos 5xcos x+5(2cos 3xcos x)+102cos2 xcos 5x+5cos 3x+10cos x =2cos x
dydx=-2sin x

ctaimg
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